JP-A-2002-260827 discloses a conventionally known glow plug. As shown in FIG. 11 of the aforementioned Japanese Patent document, the glow plug includes: a cylindrical housing 90; a heater 91 which is fixed into the housing 90, and which has a heating portion 91a projecting from the tip end of the housing 90; a rod-like inner shaft 92 which is placed in the housing 90, and in which a rear end portion projects from the rear end of the housing 90; and a pin terminal 93 which is fitted to the rear end portion of the inner shaft 92, and which is used for supplying electricity from the outside to the heating portion 91a through the inner shaft 92.
The heater 91 is a ceramic heater which is fitted into an outer sleeve 94 that is fitted to the tip end side of the housing 90, and that is made of a conductive metal, and which allows the heating portion 91a to project from the tip ends of the housing 90 and the outer sleeve 94.
The ceramic heater 91 is configured by a rod-like insulating member 80 containing Si3N4 as a major component. A U-shaped heating member 81 is embedded in the tip end side of the insulating member 80, and contains WC as a major component. A first lead wire 82 has one end connected to one end of the heating member 81, and the other end exposed from a part of the outer circumferential surface of the insulating member 80. A second lead wire 83 has one end connected to the other end of the heating member 81, and the other end exposed from another part of the outer circumferential surface of the insulating member 80. The other end of the first lead wire 82 is connected to the outer sleeve 94, that the other end of the second lead wire 83 is connected to an electric coil 95, and the electric coil 95 is connected to the inner shaft 92. The tip end side of the insulating member 80, in which the heating member 81 is embedded, functions as a heating portion 91a of the ceramic heater 91.
The pin terminal 93 has a small-diameter portion 93a in the rear end side, and a large-diameter portion 93b in the tip end side. The end surface on the rear end side of the small-diameter portion 93a has a curved surface shape. A first flange 93c, which abuts against an insulator 96 that is disposed on the rear end side of the housing 90 and that is made of an insulating material, is formed on the tip end side of the large-diameter portion 93b. A second flange 93d is formed on the rear end side of the large-diameter portion 93b. An engagement portion 93e, that engages an engagement convex portion 85a of a cap 97 to which electricity is supplied from the outside, is formed between the first flange 93c and the second flange 93d. 
In the glow plug, the heating portion 91a of the ceramic heater 91 is located in a combustion chamber of a diesel engine by screwing a male thread 90a of the housing 90 to a cylinder head of the diesel engine. Then, the housing 90 is grounded to the cylinder head, and the cap 97 which leads to a battery, is fitted to the pin terminal 93. The cap 97 is configured by a cup-shaped cap body 85, and an electric conductive member 87 which is fixed, for example, in a state where the electric conductive member extends from the inner side toward the opening side, by a fixing member 86 that is disposed in the inner side of the cap body 85. An engagement convex portion 85a which inwardly projects is formed in the opening side of the cap body 85. The electric conductive member 87 is connected to a lead wire 88 which leads to the battery.
When the cap 97 is fitted to the pin terminal 93, the engagement convex portion 85a of the cap body 85 overrides the second flange 93d to be engaged with the engagement portion 93e. In the state, the electric conductive member 87 abuts against the surface of the small-diameter portion 93a. 
In the ceramic heater 91, therefore, a voltage is applied between: the housing 90, the outer sleeve 94, and the first lead wire 82; and the pin terminal 93, the inner shaft 92, the electric coil 95, and the second lead wire 83, and heating portion 91a generates heat by means of the heating member 81. Therefore, starting of the diesel engine is initiated.
According to the publication, a glow plug of this kind is produced in the following manner. Namely, the housing 90, the ceramic heater 91, the inner shaft 92, and the like are first produced. Furthermore, the pin terminal 93 is produced by applying a cutting process to a workpiece made of steel. While required places of these components are electrically connected to one another, then, these components are assembled together, and a glow plug is completed.
In the method of producing a glow plug, however, the pin terminal is produced only by the cutting process performed on the workpiece. Therefore, swarf is excessively wasted, the time period required for production is long, and mass production is difficult. In the conventional production method, therefore, reduction of the production cost of a pin terminal is difficult. Accordingly, also reduction of the production cost of a glow plug is difficult.
The applicant of the present application has filed a patent application related to a method of producing a pin terminal for a glow plug, and method of producing a glow plug which can solve the problems, and obtained a patent on the production methods (Japanese Patent No. 4,241,489). In the production methods, small- and large-diameter portions, first and second flanges, and engagement portion of a pin terminal are formed by a plastic working on a workpiece.
According to the production methods, as compared with the case where a pin terminal is produced only by applying a cutting process to a workpiece, swarf is reduced, and the time period required for production can be shortened. Therefore, mass production is facilitated. According to the production methods, therefore, reduction of the production cost of a pin terminal is realized, and consequently reduction of the production cost of a glow plug is realized.
Also in the production methods, however, the first flange is formed in the tip end of the large-diameter portion, and the second flange is formed in the rear end side of the large-diameter portion in a similar manner as the pin terminal 93 of FIG. 11. In the pin terminal, therefore, a to-be-crimped portion which is formed to have the even outer diameter, and which is capable of being crimped is limited between the first flange and the second flange, and becomes short. In the short to-be-crimped portion, therefore, the inner shaft and the pin terminal are unlikely to be firmly coupled together. Therefore, the coupling strength between them must be ensured by employing a longish inner shaft. In the pin terminal, therefore, reduction of the material has not been sufficient, and also reduction of the weight has not been sufficient. Also in a glow plug, since such a pin terminal is employed, and a longish inner shaft is employed, reduction of the material has not been sufficient, and also reduction of the weight has not been sufficient.
The invention has been conducted in view of the above-discussed circumstances. It is a problem to be solved to enable a high-quality and light-weight pin terminal for a glow plug, and consequently a high-quality and light-weight glow plug to be economically produced.
In accordance with the present invention, there is provided a method of producing a pin terminal for a glow plug, the method comprising:
obtaining a first workpiece which has a rod-like shape, and which is made of the conductive metal;
plastically deforming an end surface of a rear end side of the first workpiece into a curved surface shape to obtain a second workpiece;
plastically deforming a rear end side of the second workpiece into a small-diameter portion which is configured to be fitted to a cap for supplying electricity from an outside, and plastically deforming a tip end side of the second workpiece into a large-diameter portion which is larger in diameter than the small-diameter portion to obtain a third workpiece; and
plastically deforming a flange between the small-diameter portion and the large-diameter portion, the flange being larger in outer diameter than the large-diameter portion, and an engagement portion formed between a position where a diameter of the flange is maximum and the large-diameter portion, an outer diameter of the engagement portion being gradually reduced toward the large-diameter portion, and the engagement portion being configured to be engaged with the cap to obtain a fourth workpiece.
Also in the production method of the invention, the small-diameter portion, large-diameter portion, flange, and engagement portion of the pin terminal are formed by applying a plastic working to a workpiece in a similar manner as the above-described production method of Japanese Patent No. 4,241,489 issued to the applicant.
In the production method, moreover, the fourth workpiece which has the flange between the small-diameter portion and the large-diameter portion, and which does not have a flange in the tip end of the large-diameter portion is produced. When a pin terminal is produced by the production method, as compared with a conventional pin terminal which has the same total length, and in which the length from the tip end to the engagement portion is identical, therefore, the to-be-crimped portion which is formed to have the even outer diameter, and which is capable to being crimped is extended. Even when a shortish inner shaft is employed, therefore, the crimped portion which is actually crimped can be extended because of the to-be-crimped portion which is longer than a conventional one, and the inner shaft and the pin terminal are likely to be firmly coupled together.
In the pin terminal, moreover, reduction of the material can be sufficiently performed correspondingly with the configuration where a flange is not formed in the tip end of the large-diameter portion, and also reduction of the weight can be realized. A glow plug can employ such a pin terminal, and a shortish inner shaft can be employed. Also in a glow plug, therefore, reduction of the material can be sufficiently performed, and also reduction of the weight can be attained.
In the production method, moreover, a flange is not formed in the tip end of the large-diameter portion, and hence it is not necessary to employ a split die which is radially divided in the periphery of the large-diameter portion. According to the production method, therefore, the structure of the die is simplified, the production cost of the die can be lowered, and the durability of the die can be improved.
According to the production method of the invention, it is possible to economically produce a high-quality and light-weight pin terminal for a glow plug, and consequently a high-quality and light-weight glow plug.
In the production method of the invention, in at least one of the step of deforming the end surface, the step of deforming the rear end side and the step of deforming the third workpiece, a fitting recess to which a rear end portion of an inner shaft of the glow plug is fitted is formed in an end surface of the tip end side of the pin terminal. In this case, the steps which are performed until the processing of the fourth workpiece, including molding of the fitting recess are performed by a plastic working. Also during the molding of the fitting recess, therefore, swarf is not produced.
In this regard, in the case where the pin terminal is produced only by applying a cutting process to a workpiece, or where the formation of the fitting recess is produced by a cutting process, swarf is produced. Since there is a possibility that swarf may cause the inner shaft to be hardly fitted to the fitting recess, and that a short circuit may occur, swarf has to be removed away. However, this work for removing the swarf requires great labor. In a pin terminal which is obtained by employing a split die, furthermore, the large-diameter portion is liable to have radial burrs, and the work of surely removing the burrs in order to prevent a situation where the burrs are peeled off to cause a short circuit, from occurring similarly requires great labor. In the production method, by contrast, the amount of swarf can be made minimum, and burrs are hardly produced. Even when labor of removing swarf and burrs is not so much provided, therefore, the assembling property of the glow plug can be improved, and the short circuit caused by the pin terminal can be avoided.
When the steps of processing from the workpiece to the fourth workpiece through the second and third workpieces are performed by a plastic working, moreover, the process time in the process from the first workpiece to the fourth workpiece can be shortened. When the plastic working is performed as described above, for example, a large number of second workpieces can be simultaneously processed to third workpieces, and then to fourth workpieces. Therefore, pin terminals are easily mass produced. Because of these, when a pin terminal is produced as described above, reduction of the production cost thereof can be further realized, and consequently reduction of the production cost of a glow plug can be further realized.
In the production method, as described above, swarf is not produced during the molding of the fitting recess. Since, in the steps of processing from the first workpiece to the fourth workpiece, swarf due to the respective workpieces is not produced, the method can contribute to realization of further resource saving.
In the step of deforming the end surface, a first fitting recess having a first depth may be formed in an end surface on a tip end side of the first workpiece. In the step of deforming the rear end side, a second fitting recess having a second depth which is deeper than the first depth may be formed in an end surface on a tip end side of the second workpiece. In the step of deforming the third workpiece, the fitting recess having a third depth which is deeper than the second depth may be formed in an end surface on a tip end side of the third workpiece.
In this case, in the first to third workpieces, the fitting recess is formed respectively in a plurality of steps so that its depth becomes deeper in the sequence from the first fitting recess to the fitting recess. Therefore, even when the shape of the first fitting recess formed in the first workpiece is deformed in the other subsequent steps, the shape can be corrected when the second fitting recess is formed in the second workpiece. According to the production method, therefore, the shapes of fitting recesses of produced pin terminals are easily homogenized.
The fitting recess may be configured by a cylindrical inner circumferential surface which extends from a tip end of the large-diameter portion toward a rear end, and an upper bottom surface which is continuous to a rear end of the inner circumferential surface. The upper bottom surface may have a tapered shape in which a diameter becomes smaller toward a rear end side.
According to the inventor's confirmation, because of an affection of plastic deformation of the third workpiece in the formation of the flange, strain or the like easily occurs in the upper bottom surface of the fitting recess, and wrinkles or the like caused by the strain are easily formed in the upper bottom surface. On the other hand, a plating process is applied to a pin terminal of a glow plug for the purpose of protection of the surface thereof. In the case where strain occurs in the upper bottom surface, therefore, a washing solution or the like which is used in the plating process remains in the wrinkles or the like in the upper bottom surface, and therefore the quality of plating in the fitting recess is liable to be lowered. Because of the affection of the remaining washing solution or the like, rust or the like is easily formed on the upper bottom surface. Because of these, the quality of a pin terminal is liable to be lowered.
Therefore, according to one aspect of the present invention, the upper bottom surface of the fitting recess is formed into a tapered shape in which the diameter becomes smaller toward the rear end side, whereby, in the third workpiece in which the fitting recess is formed, the thickness of the circumference of the upper bottom surface is made large. Therefore, the upper bottom surface is hardly (barely) deformed even by plastic deformation in the formation of the flange, and strain or the like hardly occurs in the upper bottom surface. Therefore, a washing solution or the like hardly remains on the upper bottom surface, and plating is satisfactorily applied to the fitting recess. Moreover, also rust or the like is hardly formed on the upper bottom surface. Because of these, the quality of a pin terminal is high.
Furthermore, it is preferable that the upper bottom surface is positioned on a tip end side of the fourth workpiece with respect to the maximum diameter position of the flange. The plastic deformation of the third workpiece in the formation of the flange is largest at the maximum diameter position of the flange. When the upper bottom surface of the fitting recess is positioned on the tip end side of the fourth workpiece with respect to the maximum diameter position of the flange, the influence of the plastic deformation on the upper bottom surface can be further reduced. Therefore, deformation of the upper bottom surface due to plastic deformation hardly occurs, and the pin terminal has a higher quality.
Preferably, the flange has: a first cylindrical surface which is positioned on a side of the small-diameter portion, which is larger in diameter than the small-diameter portion, and which is cylindrical; a convexly curved surface which is connected to the first cylindrical surface, and in which an axial section is arcuate, and a section in a direction perpendicular to an axis is circular; and a second cylindrical surface which is connected to the convexly curved surface, which is equal in diameter to the first cylindrical surface, and which cylindrical. Preferably, the flange has: a first disk surface which is connected to the small-diameter portion, and which extends in the direction perpendicular to the axis; a tapered surface which is connected to the first disk surface, in which a rear end side has a smaller diameter, and which is connected to the first cylindrical surface; and a second disk surface which connects the second cylindrical surface to the large-diameter portion, and which extends in the direction perpendicular to the axis.
In these cases, the convexly curved surface or the tapered surface causes the cap to be easily fitted to the pin terminal. Moreover, the second cylindrical surface causes the cap engaged with the engagement portion to hardly slip off from the pin terminal.
In the production method of the invention, a first die having a first cavity which can mold a rear end side of the convexly curved surface, and a second die having a second cavity which can mold a tip end side of the convexly curved surface may be used. In the first die and the second die, preferably, a parting surface between the first cavity and the second cavity is on a tip end side with respect to the maximum diameter position, and a maximum diameter of the second cavity is smaller than a maximum diameter of the first cavity.
Because of the difference between the maximum diameter of the first cavity and that of the second cavity, in the convexly curved surface formed by the first die and the second die, the side having an arc directed from the parting surface to the first cylindrical surface, and that the side having an arc directed from the parting surface to the second cylindrical surface are different in diameter from each other, with the parting surface as the boundary. Because of the difference between the diameters, in the outer circumferential surface of the convexly curved surface, a step is formed on the tip end side with respect to the maximum diameter position. Therefore, the cap can be engaged with the step. In a pin terminal which is produced by the above-described production method, therefore, the cap can be satisfactorily fitted.
In the case of a pin terminal, in which another engagement portion is disposed on the tip end side of the pin terminal with respect to the step and the cap is to be engaged with the engagement portion, even when the cap is caused to be disengaged from the engagement portion by vibrations or the like, and the cap is moved in the direction along which the cap slips off from the pin terminal, the cap is caused to be engaged with the step. In such a pin terminal, namely, a state is attained where the cap is doubly engaged by the engagement portion and the step, the cap can be further satisfactorily fitted.
In the production method of the invention, the step is formed by using a diameter difference between the maximum diameter of the first cavity and the maximum diameter of the second cavity. Therefore, as compared with the case where a step is formed by a cutting process on the whole outer circumferential surface of the convexly curved surface, for example, production of swarf from the workpiece can be suppressed.
Preferably, the production method of the invention further has an outer diameter finishing step of finishing the outer diameter of the fourth workpiece by performing cutting or polishing in which a cutting depth is 1 mm or less, to form the pin terminal. In this case, the fourth workpiece can be produced in a relatively rough manner, and the production of the fourth workpiece is facilitated. Then, a pin terminal with higher accuracy can be produced by performing cutting or polishing on the fourth workpiece. When the cutting depth is 1 mm or less in this case, cutting swarf or polishing swarf caused by cutting or polishing can be reduced. Therefore, resource saving and reduction of the production cost can be realized without impairing the effects of the invention.
The method of producing a glow plug according to the invention is a method of producing a glow plug including: a cylindrical housing; a heater which is fixed into the housing, and which has a heating portion projecting from a tip end of the housing; a rod-like inner shaft which is placed in the housing, and in which a rear end portion projects from a rear end of the housing; and a pin terminal which is fitted to the rear end portion of the inner shaft, which is used for supplying electricity from an outside to the heating portion through the inner shaft, the method comprising:
obtaining a first workpiece which has a rod-like shape, and which is made of the conductive metal;
plastically deforming an end surface of a rear end side of the first workpiece into a curved surface shape, and setting to a second workpiece;
plastically deforming a rear end side of the second workpiece into a small-diameter portion which is configured to be fitted to a cap for supplying electricity from an outside, and plastically deforming a tip end side of the second workpiece into a large-diameter portion which is larger in diameter than the small-diameter portion to obtain a third workpiece; and
plastically deforming the third workpiece to form a flange between the small-diameter portion and the large-diameter portion, the flange being larger in outer diameter than the large-diameter portion, and an engagement portion formed between a position where a diameter of the flange is maximum and the large-diameter portion, an outer diameter of the engagement portion being gradually reduced toward the large-diameter portion, and the engagement portion being configured to be engaged with to obtain a fourth workpiece.
The glow plug which is obtained by the production method of the invention includes a pin terminal including the features of claim 1 above. The glow plug which is obtained by the production method is light weight and economical, and its durability is enhanced because the inner shaft and the pin terminal are fastened to each other with a crimping area which is larger than a conventional one owing to the extended crimped portion. Therefore, its durability is enhanced.
In the glow plug, as compared with a conventional glow plug, a portion of the inner shaft which projects from the rear end of the housing can be shortened, and the whole inner shaft can be shortened. Therefore, reduction of the weight of the glow plug can be realized.
According to the production method of the invention, therefore, a high-quality and light-weight glow plug can be economically produced.
According to the production method of the invention, a high-quality and light-weight pin terminal for a glow plug or glow plug can be economically produced.